I. Field of the Invention
This invention is directed to actinic radiation curable polymers. More particularly, this invention is directed to a novel class of photosensitive polymers which are formed by the reaction of certain polymers with halogenated cyclic anhydrides and glycidyl esters of alpha, beta-unsaturated carboxylic acids. The resulting photosensitive polymers are capable of undergoing rapid curing or crosslinking on exposure to actinic radiation and have particular use in the preparation of photosensitive compositions.
II. Brief Description of the Prior Art
It is well known that actinic curable compositions generally comprise a low molecular weight polyunsaturated resin dissolved in a selected combination of vinyl monomers to which a relatively small amount of photoinitiator is added. The resultant composition is then coated on a substrate and cured by exposure to actinic radiation, thereby forming a high molecular weight polymer on the substrate.
It has previously been found desirable, for fast and efficient curing of such polymers, to include within the system relatively large amounts of the photoinitiating component. Such levels of photoinitiator cannot, however, be used with certain systems since these high levels of photoinitiator will not dissolve or mix homogeneously with the remainder of the system. Even in systems wherein these larger amounts of photoinitiators are compatible, most of the photoinitiator will remain chemically unbonded in the final cured composition producing deleterious effects on the properties of these cured materials. An additional drawback to the use of high levels of photoinitiators is the possibility of the occurrence of side reactions by the unbonded portions of the photoinitiators on exposure to actinic radiation. Furthermore, in systems which require additional reagents, such as synergists to effectively initiate polymerization, the presence of the necessary correspondingly high concentrations of these synergistic chemicals would also result in a reduction of the desired properties of the cured compositions. Still an additional drawback to the addition of such post-added synergists is the fact that even after curing the synergists may not be permanently bonded within the system and may leach out and cause undesirable contamination in the final composition.
Recently, monomeric photoinitiators have been proposed wherein the photoinitiating component becomes permanently incorporated into the backbone of the final cured polymer thereby avoiding many of the drawbacks discussed above. In these cases, the monomeric photoinitiator is randomly bonded with specific copolymerizable monomeric materials and the resultant relatively low molecular weight prepolymeric compound is cured by exposure to actinic radiation. Alternatively, these monomeric or prepolymeric photoinitiators may be chemically bonded by conventional polymerization techniques to other monomeric or polymeric compositions prior to exposure to radiation. In either of these embodiments, however, the practitioner's choice of monomers has been limited mainly to polyfunctional acrylate and methacrylate based monomers since most monomers, particularly those monofunctional acrylates and methacrylates which would result in a flexible soft coating, are slow to cure, have undesirable odors and/or are toxic in their uncured state. Thus, the final properties in the cured compositions have been limited primarily to rigid, non-flexible coatings or shaped articles.
Therefore, in order to produce photosensitive polymeric compositions, particularly those resulting in flexible or soft cured coatings or articles, the practitioner has been restricted to post-adding photoinitiators to the polymer, often in conjunction with synergistic chemicals. The problems inherent in this method are comparable to those encountered when post-adding photoinitiators to monomers discussed above.
It is an object of the present invention to provide high molecular weight photosensitive polymers capable of undergoing rapid crosslinking and curing when exposed to actinic radiation.
It is a further object of the invention to provide photosensitive polymers which contain a wide range of polymeric backbone components thereby enabling formation of a wide variety of properties in the final cured material.
It is also an object of the invention to provide photosensitive polymers which will cure rapidly when exposed to actinic radiation without the necessity for or the addition of post-added and externally unbonded photoinitiator and/or synergistic chemical.
It is an additional object of the invention to provide a novel class of photosensitive polymers which are relatively insensitive to the effects of atmospheric oxygen and which will cure rapidly and efficiently when exposed to actinic radiation.
These and other objects will be apparent from the description which follows.